The present invention is directed to a method for preserving plants and plant parts using new preservative materials that reduce bleeding of the preservatives when the preserved plants are subjected to high humidity conditions. The invention is also directed to the preserved plants produced by the method.
In recent years a significant new industry has sprung up based on improved technology for preserving plants. These processes give very high quality, natural appearing products. Preserved plants are used in environments that might be marginal or unsuitable for living plants, or where the care and maintenance of living plants would be too costly or impractical. A wide number of different types of plants have been offered to date. These vary from floral arrangements, to small foliage-type shrubs, all the way to small trees up to about 6-7 meters high.
In one process, the plants are cut above the root line and the stem is immersed in a treating solution which is perfused into the plant by natural fluid transport processes. Environmental temperature and humidity are carefully controlled during the treatment time, which can last up to two weeks. Glycerol is almost universally used as the preservative material, along with minor amounts of salts for osmolality and/or pH control, and water soluble dyes.
The processes outlined in Nordh, U.S. Pat. No. 4,243,693, can be said to be typical of the present state of the art. Nordh describes an aqueous preservative solution having from 18-35% by volume of glycerol and 2-10 g/L of the yellow food dye tartrazine. The dye is said to be a critical component of the composition if optimum preservation is to be obtained. The solution also contains 1-15 g/L of KNO.sub.3 as well as minor amounts of a blue dye to produce a preferred green color. Treatment of the plants is carried out in an environment in the range of 15.degree.-33.degree. C. in air which is at most no greater than 60% relative humidity.
Sellegaard, in U.S. Pat. No. 4,710,394, teaches a very similar preservative system to that described by Nordh. The exception is the inclusion of 1-6% of an organic acid, preferably citric acid, in the preservative solution. One other difference is his use of a treatment temperature range for some products well above that described by Nordh as being critical. A major claim to novelty by Sellegaard is that the dry chemicals in his mixture are packaged separately and combined with glycerine and water at the point of use.
Reference is made here to an earlier application commonly assigned with the present one. This describes treatments which produce flame retardant plants, especially useful in public places where fire hazard must be kept to an absolute minimum. This application, Ser. No. 113,312, filed Oct. 28, 1987, is hereby incorporated by reference.
In addition to the process of perfusion, a number of inventors have taught immersion of the entire plant being treated in a bath containing glycerine as the principal preservative. These include Segall, U.S. Pat. No. 1,410,226, who directs his process to the preservation of ferns. These are first treated in a caustic solution, bleached, and then dyed by immersion in a warm solution of dye, glycerine, alcohol, and water.
In U.S. Pat. No. 1,484,656, to Koroff et al., the plants are first dried and then placed in a preserving solution of glycerine, water, and formalin.
Dux, in U.S. Pat. No. 2,026,873, describes a preservative solution containing glycerine, a vegetable gum, sodium benzoate, and water soluble sulfonated vegetable oil. In contrast to most of the other processes, Dux submerges his plants for only a few minutes whereas the other processes described to this point need many hours or days.
U.S. Pat. No. 3,895,140, to Sheldon et al, teaches preservation of cult foliage by immersing it in a relatively hot solution of glycerine or polyglycerine at temperatures in the range of 60.degree.-82.degree. C. or even higher. The inventors note that a number of other polyols including trimethylolpropane, propylene glycol, sorbitol and pentaerythrytol were not effective as preservative materials.
Romero-Sierra et al, in U.S. Pat. No. 4,278,715 and 4,328,256, describe a very complex mixture and process for preserving plant specimens. The treatment solutions contain a diol or triol such as ethylene glycol or glycerine but also require many other materials, including a lower carboxylic acid as a preservative. The main advantage taught by these inventors is that the natural green color is preserved. However, it is apparent that the specimen is usable only for a period of a few weeks without additional treatment. To get permanent preservation, this second treatment involves immersion in a solution of 100-700 mL of glycerine per liter for a period two to three weeks, or even permanently, at ambient conditions.
French Pat. No. 2,160,310 teaches preservation of cut foliage by immersion in a solution containing one third glycerine and two-thirds water.
A number of other patents might be cited in which a polyol preservative is either not required or is present as an optional ingredient. These include U.S. Pat. No. 1,714,838 to Anderson, which describes the use of calcium chloride as a plant preservative.
Ruzicka, in U.S. Pat. No. 1,908,922, describes treatment with a sucrose solution for extending the life of cut flowers. This inventor makes no claim to permanent preservation, however.
Fessenden, in U.S. Pat. No. 2,978,348, teaches preservation by immersing foliage in a solution which includes a water soluble salt of aluminum, an alkaline salt of an acid which will form insoluble salts of aluminum under alkaline conditions, and a volatile organic acid to reduce the pH until the plant is withdrawn from the treating solution. The solution may contain a humectant which is a neutral salt of an aliphatic amine or it may optionally include polyols such as glycerol, sorbitol, or polyethylene glycol 200. The polyols appear to be an optional and a minor part of the formulation and their specific function or purpose is not disclosed.
Along with the increased popularity of preserved plants a problem has now been recognized which, until the present time, has not been dealt with in the related literature. This is the matter of bleeding of the preservative materials from the leaves and stems of the treated plant. Ordinarily this is not a serious problem. However, it may become one after the plant is exposed for protracted periods in which the humidity is very high. Very high humidity is a common summer condition in the eastern and Gulf Coast portions of the United States and in other areas of the world. The bleeding is unsightly because it gives the affected portions a wet, sticky appearance and may encourage the growth of molds or fungi. In some cases bleeding may become so severe that droplets of preservative actually fall from the plant onto the floor. These droplets carry with them the water soluble dyes used for control of foliage color. Permanent staining of carpets or other flooring material has occasionally resulted during these extreme bleeding situations.
The present invention deals with treatment methods and new preservative materials which greatly reduce or completely overcome the problem of bleeding, even after relatively prolonged exposure to high humidity conditions.